In the new era of wireless communication, various kinds of high technological communication devices have been constantly introduced into the market to create prosperous development in the business of communication products. Among others, mobile devices have the advantages of being portable and convenient for use and therefore have become the major communication devices among consumers. Further, to meet the consumers' demand for multifunction, the conventional dual-frequency mobile communication devices have also been replaced by the new multi-frequency mobile communication devices.
An antenna is a microwave device that is particularly designed for propagating electromagnetic energy in a specific direction. The antenna is mainly used to effectively radiate a signal from a transmitter into a free space or to effectively couple a remotely transmitted electric signal to a receiver. Therefore, an antenna is considered a transducer. Currently, the antennas built in common mobile devices include the following several types: monopole antenna, dipole antenna, planar inverted-F antenna (PIFA), and loop antenna.
The monopole antenna and the dipolar antenna are characterized in their considerably good transmitting and receiving power. However, they have the problem with SAR (Specific Absorption Rate) test and often fail to satisfy the electromagnetic wave energy absorption rate test.
The planar inverted-F antenna (PIFA) is advantageous for use in a product having very limited internal space and can be built in the mechanism to give the product a beautiful appearance. However, it often has relatively short transmission range when being used in some complicated space.
The loop antenna is usually used in high-frequency signal transmission. However, it has high input impedance and therefore can not be applied to small-sized communication devices.
FIG. 1 shows a prior art full-band internal antenna developed for mobile communication devices. This type of full-band internal antenna is provided on a dielectric layer 10 and includes a first radiation section 11 and a second radiation section 12. The first radiation section 11 has an end being extended to form a branch section 13 for electrically connecting to a short-circuit portion 14. The branch section 13 further includes an adjustment section 15. The second radiation section 12 is rightward extended to form an extended section 16, and is leftward extended to form a long arm portion 17, which is parallel to the first radiation section 11. To comply with the relevant telecommunication codes, the currently designed antennas generally have two types of relatively large sizes, that is, 80×13×0.4 mm and 70×13×0.4 mm. However, antennas with these two types of sizes could no longer match the nowadays multifunctional and miniaturized mobile devices.
It is therefore necessary to provide an internal antenna structure that employs a spiral design and a multi-coupling mechanism to enable miniaturized antenna size and receipt of multiple frequencies while complying with relevant telecommunication codes.